The decision about whether to abort should ultimately be the host's. There may be exceptions, but that should be the default. Until it is born, the embryo/fetus is part of the woman's body, and she therefore should have the right to decide what to do with it.
Euthanasia should be legal, although there needs to be some kind of procedure to prevent either abuse (e.g. trying to cash in on a rich relative) or needless suicide (e.g. someone believing a situation is hopeless when in fact there is a solution).
As far as life being sacred... I think if anything is sacred, it is the spirit or soul (which I use to mean something like "the personality characteristics that define who someone can be"), not the sheer "life" (metabolism) of the spirit's container (body).
I propose the following principles:
- Every spirit deserves a vessel (body) worthy of it. (The spirit (soul/mind) deserves a body which is physically able to support the spirit, without chronic pain or excessive maintenance, and carry out the spirit's wishes within reason.)
- A new spirit deserves to be born into a community that wants it and has the ability to care for it adequately until it is able to care for itself.
- Every spirit has the right to choose to end itself.
- If the spirit is too new to be able to make or express its life decisions, then the parents (or the community) must make those decisions.
For all the moral high ground currently being claimed by the "pro-life" movement, they're elevating the body to a position of sacredness and totally ignoring that which ought to be far more important, i.e. the person inside.
Overall, we need to balance our compassionate wish to preserve life against our compassionate wish not to cause suffering. Those twin considerations should override any arbitrary sacredness of human life at any age. Any life decision depends heavily on context, including the wishes of the life in question (at which we can only make an educated guess in some cases), and should not be decided arbitrarily based on any hard-and-fast rule.
(This leaves open a lot of issues which need to be addressed, such as when do parents abandon their right of choice, when is a parental decision out of bounds, etc. but at least gives some basis from which those decisions can be made.)